The second motorcycle I owned appealed to me in part because of the sound: it had what people call a "throaty roar." (It was a Yamaha, but I suspect it had been engineered to sound Harley-esque.) In spite of this, I didn't really start to love riding the bike until I added an essential accessory: earplugs.

A sad effect of getting older is that loud sounds tend to bother you more than they did in your rock-n-roll youth. Possibly I would have enjoyed the unfiltered and aforementioned roar as a 19-year-old, but by the time I got the bike, I was covering my ears for passing sirens and babies shrieking nearby. But even as a 19-year-old with perfect hearing, it would have been a very good idea to wear plugs to save my hearing.

To state the obvious, (some) motorcycles are loud. The engine can emit anywhere from 80 decibels at normal speed to 100 dB when you rev it. That's louder than a lawnmower, and well into territory where hearing protection is recommended or, depending on your work, mandated. This is loud even to people who are on the curb while a motorcycle passes. The rider, of course, is about a meter away from the source of this noise, sometimes for hours.

Why are some motorcycle engines so loud? Well, one reason is that some people are just going to want to be loud, and obnoxiousness either isn't a factor for them or is the actual point.

Some people argue that a louder bike has better performance. This is true in a narrow sense: the shorter and less obstructed the exhaust path (hence, the louder the bike), the better the horsepower, by a small degree. However, whether there are other options for increasing horsepower, or whether a rider actually needs the extra horsepower, and whether the increased horsepower is actually the goal of the louder exhaust—well, these are points that one would need to discuss with individual riders. Cite from an online forum: And of course, Harley Davidsons just need louder pipes because yea. :)

Another argument for noise is the clichéd refrain "Loud pipes save lives"—that being loud makes other drivers aware of your presence. As a cranky article points out, that would be more true if the pipes faced forward, rather than annoying the people you've passed. And that there are many other, albeit dorkier, ways to raise one's visibility, including extra lighting and high-conspicuity jackets and helmets. Not to mention that modern cars have very good soundproofing. And that many motorcycle accidents would not have been prevented by noise; many are in fact are caused by the rider.

But even without deliberate efforts to make a motorcycle engine loud, it's just, well, loud.

Another and less obvious source of dangerous levels of noise is wind. A motorcycle rider on the freeway is literally sitting in 60-mph winds or, er, higher. (A windshield routes some of this airflow around you, of course, but doesn't eliminate it completely.) One article estimates that wind noise at 65 mph can reach 100 dB:

You might think that having a helmet on would alleviate this noise, but it can actually add to it; the wind whipping over and (especially) under a helmet can cause very high levels of noise. As one motorcycle site says:

It is our considered opinion, based on many years of evaluating dozens of different motorcycle helmet of all types and talking to experts in the field that there are basically only two types of motorcycle helmets: loud and louder.

The inevitable conclusion for anyone who wants to save their hearing (in my case, what's left of it) is that earplugs should be essential gear for every ride. I keep a handful of foam earplugs in a pocket of my motorcycle jacket, and have over the years developed the habit of cramming one in each ear before putting on my helmet. (Until I did this reflexively, I sometimes would have to take my helmet off again to put in earplugs, but I never skipped this step.)

One might have some concerns that wearing earplugs while driving is itself dangerous; shouldn't you be able to hear traffic noise and sirens and stuff? Yes, you should. (That said, see the earlier comment about the noiseproofing in modern cars.) I've found that the -20 dB or so reduction afforded by the foam plugs provides good balance. I'm not deafened by my bike, but I can still hear—well enough, in fact, that I can use my Sena headset to talk on the phone (via Bluetooth) as I ride. It's also possible, tho I don't know this first hand, that there are ear plugs that are tuned to eliminate primarily engine and wind noise but still allow clarity for other sound.

I do get the appeal of the throaty roar, as noted at the beginning, and I even like the sound of Harleys, as long as I'm not too close. But since that lovely noise can take a toll, it's essential to balance that with your own safety.